Neurostimulation has become an accepted treatment for patients with chronic pain in their back and/or limbs who have not found pain relief from other treatments. In general, neurostimulation comprises applying an electrical current to nerve tissue in the pathway of the chronic pain. This creates a sensation that blocks the brain's ability to sense the previously perceived pain. There are two conventional forms of electrical stimulation commonly used to treat chronic pain: Spinal Cord Stimulation (SCS) and Peripheral Nerve Field Stimulation (PNFS). In SCS, electrical leads are placed along the spinal cord. A programmable implantable pulse generator (IPG) is implanted in the upper buttock or abdomen (under the skin) which emits electrical currents to the spinal cord via electrodes of the leads. Peripheral nerve field stimulation is similar to spinal cord stimulation, however peripheral nerve field stimulation involves placing the leads just under the skin in an area near to the peripheral nerves involved in pain.
FIGS. 1A and 1B will now be used to illustrate how an external handheld programmer (often referred to herein as an “external programmer” or simply as a “programmer”) can be used to program and otherwise control an IPG. Referring to FIG. 1A, an IPG 112 is shown as being implanted within a patient 102. One or more leads 114, each having one or more electrodes 116, are connected to the IPG 112 for delivery of neurostimulation (e.g., spinal cord stimulation) to the patient. The electrode(s) 116 can be electrically coupled to electronic circuitry within the IPG 112 by coupling the leads 114 to connectors of the IPG 112. Where a housing (also referred to as the “case” or “can”) of the IPG 112 is electrically conductive, the housing can act as an electrode. Although not limited thereto, the lead 114 can be positioned so that the electrodes are disposed on or near a dorsal root or dorsal root ganglion. Additional details regarding such stimulation are provided in U.S. Pat. No. 7,450,993, entitled “Methods for Selective Stimulation of a Ganglion”, and U.S. patent application Ser. No. 12/607,009, entitled “Selective Stimulation Systems and Signal Parameters for Medical Conditions”, both of which are incorporated herein by reference.
FIG. 1A also shows an external handheld programmer 122 that can be used to program and/or otherwise control the IPG 112. There are generally two types of programmers, both of which can be handheld and capable of wireless communication with the IPG 112. One type of programmer 122, that is used by a representative of the IPG manufacturer, a clinician, a physician and/or other medical personnel (collectively referred to hereafter as a “programming person”), is often referred to as a “clinician programmer”. FIG. 1A illustrates a programming person 104 holding the programmer 122, which can be a clinician programmer. The other type of programmer 122 is often referred to as a “patient programmer” because it is primarily intended to be controlled by the patient within which the IPG is implanted. FIG. 1B illustrates the patient 102 holding the programmer 122, which can be a patient programmer. While a clinician programmer is typically more complex and typically has greater capabilities than a patient programmer, for the purpose of this discussion both types of programmers can be referred to interchangeably.
The programming of the IPG 112 performed using a clinician programmer can include identifying and storing one or more neurostimulation parameter sets that treat a targeted pain of a patient. This often requires the interaction of the programming person 104 and the patient 102. Typically while handholding the programmer 122, e.g., as shown in FIG. 1A, the programming person 104 manually adjusts the various stimulus parameters via a user interface of the programmer 122. Such a user interface is usually associated with a front surface of the programmer, but that is not to say that some buttons or the like may also be located on other surfaces of the programmer (e.g., the left or right sides). The patient 102 can give feedback (e.g., verbal feedback) to the programming person 104 as the programming person 104 cycles through the parameters. For example, after each parameter change made by the programming person 104, the programming person 104 may ask the patient 102 for efficacy feedback.
Each such neurostimulation parameter set that is programmed can define electrode parameters and neurostimulation signal parameters. The electrode parameters of each neurostimulation parameter set can define which electrodes are used to provide neurostimulation. Additionally, the electrode parameters of each neurostimulation parameter set can define which one or more electrodes used to provide neurostimulation are connected as a cathode, and which one or more electrodes used to provide neurostimulation are connected as an anode. The neurostimulation signal parameters of each neurostimulation parameter set can define a value for each of pulse width, pulse amplitude and pulse repetition rate, but are not limited thereto.
The programmer 122 (whether a clinician or patient type programmer) can also be used to select among a plurality of different stored neurostimulation parameter sets. Additionally, the programmer 122 can also be used to adjust neurostimulation signal parameters, e.g., to increase or decrease pulse amplitudes. For example, as shown in FIG. 1B, the patient 102 can hold a patient programmer type external programmer 122 in their hands, and use buttons, or the like, to select a specific neurostimulation parameter set and adjust the pulse amplitude corresponding to the selected set.
The programmer 122 will most likely communicate with the IPG 112 using the Medical Implant Communication Service (MICS) standard, which was defined by the U.S. Federal Communications Commission (FCC) and European Telecommunications Standards Institute (ETSI). The MICS standard uses a frequency band between 402 and 405 MHz to provide for bi-directional radio communication with medical implants, such as the IPG 112. The maximum transmit power allowed by the MICS standard is very low, with the maximum allowed equivalent isotropically radiated power (EIRP) being only 25 microwatts, in order to reduce the risk of interfering with other users of the same band. The MICS standard gives a maximum range of a couple of meters. By contrast, the maximum EIRP allowed for mobile phones and other mobile devices is typically orders of magnitude greater than the maximum EIRP allowed by the MICS standard.
The programmer 122 is typically designed so that a person handholding the programmer can properly view and interact with the user interface of the programmer when the programmer is handheld in its predetermined intended orientation, e.g., handheld at any angle between when a front surface (with which the user interface is associated) of the programmer is generally parallel to the ground (as in FIGS. 1A and 1B) and generally perpendicular to the ground. For example, referring position a in FIG. 1C, if the person were to handhold the programmer 122 at about waist level, the person may handhold the programmer so that the front surface of the programmer (and thus the user interface associated with the front surface) is facing upward and generally parallel to the earth's surface. For another example, referring position e in FIG. 1C, if the person were to handhold the programmer 122 at about eye level, the person may handhold the programmer so that the front surface of the of the programmer (and thus the user interface associated with the front surface) is facing sideways and generally perpendicular to the earth's surface. Still referring to FIG. 1C, the person may alternatively handhold the programmer 122 at other positions (e.g., positions b, c or d) that result in the front surface of the programmer (and thus the user interface associated with the front surface) being somewhere between parallel to the earth's surface and perpendicular to the earth's surface. So long as a person handholds the programmer such that the front surface of the housing is at any angle between and inclusive of parallel to the earth's surface and perpendicular to the earth's surface, which enables the person to view and interact with the user interface of the programmer in the predetermined intended manner, the programmer can be said to be handheld in its predetermined intended orientation. In other words, the predetermined intended orientation of the programmer can encompass a range of positions at which the programmer is intended to be held for use in its intended manner. It is also noted that the person may rest the handheld programmer on their lap, on a table, or on any other surface rather than handholding to device wherein such positioning of the device enables the person to view and interact with the user interface of the programmer in the predetermined intended manner.
Reference will now be made to FIG. 2, which illustrates an exemplary housing 252 of the programmer 122, with a front of the housing removed so that some components located within the housing 252 can be viewed. Referring to FIG. 2, a single or multilayered printed circuit board (PCB) 254 is located within the housing 252. While not shown, integrated circuits (ICs), also known as chips, and/or discrete circuitry can be attached to the PCB 254 and can be interconnected as appropriate by traces, vias and/or other conductors. One of the layers of the multilayered PCB 254 can be substantially covered with a conductor, e.g., copper or some other metal, to provide a ground plane 262 for the circuitry and an antenna 250 of the external programmer 122.
FIG. 2 shows an exemplary form factor and a typical location for the antenna 250 of an external handheld programmer relative to the ground plane 262. Referring to FIG. 2, the antenna 250 is shown as a being located in the same plane as the ground plane 262 above an upper boundary of the ground plane 262 (generally along the top of the housing 252), extending from the left side of the housing 252 to the right side of the housing 252. While in FIG. 2 the antenna 250 is shown as a conductive trace having a generally square wave shape, the radiation pattern of the antenna 250 would be substantially the same as if the conductive trace were a straight wire extending from left to right above the upper boundary of the ground plane 262. This is because the square wave shape mainly has the effect of only adding to the length of the antenna 250, which affects the frequency of signals emitted by the antenna, but does not affect the radiation pattern. For this reason, for the purpose of analyzing the radio frequency (RF) radiation pattern of the antenna 250, the antenna 250 can be considered a straight wire that extends above the top boundary of the ground plane from the left side to the right side of the housing 252, as shown in FIG. 3A.
Referring now to FIG. 3A, the rectangular grid represents the PCB ground plane 262 introduced in FIG. 2. The wire parallel to extending above the top boundary of the ground plane 262 in FIG. 3A represents the antenna 250 introduced in FIG. 2. FIG. 3B illustrates the antenna radiation pattern corresponding to FIG. 3A, i.e., the radiation pattern that results when the antenna 250 is located above the top boundary of the ground plane 262. As can be appreciated from FIG. 3B, when a person handholds the external programmer 122 in its predetermined intended orientation so that the person can properly view and interact with the user interface of the external programmer 122, the maximum RF radiation (which is represented by toroidal or donut shape) is not directed toward the IPG implanted within the patient. Rather, RF radiation nulls (i.e., the minimum radiation) occur in the direction of the IPG. Thus, when a programming person 104 handholds the programmer 122 in its intended orientation there is a RF radiation null in the direction of the patient 102, potentially resulting in poor communication with the IPG 112 implanted within the patient 102. Similarly, when a patient 102 within which the IPG 112 is implanted holds the programmer 122 in its intended orientation to select a neurostimulation parameter set or adjust a neurostimulation parameter, there is also a RF radiation null in the direction of the patient 102, again potentially resulting in poor communication with the IPG 112. The inefficient and potentially ineffective use of the radiation pattern shown in FIG. 3A for communicating with an IPG is compounded by the fact that the maximum transmit power allowed by the MICS standard is very low, as was explained above.